A considerable impact occurs during the hitching of loaded railway cars to one another, generally termed "humping." During humping, railway cars are accelerated over a light elevation, or hump, so that the car gathers enough speed to be hitched on impact to other cars already coupled and sitting on a track.
This impact causes unrestrained cargo in the railway car to move toward the front (i.e., coupled) end of the railway car. Damage to the cargo can thereby occur if the cargo is not properly braced and/or cushioned. In regard to large and heavy coils or rolls of sheet metal, inadequately secured rolls can hit one another as well as collide with the car interior causing the rolls to become out-of-round. Many shippers have therefore chosen to use non-rail transportation because out-of-round rolls are typically rejected by the customer. These cargo loads have therefore generally been shipped by truck, which can substantially increase the cost of shipping.
Some of those who have nevertheless shipped by rail have loaded the railway cars by a two-step "static loading" method. Each cylindrical roll is placed in the railway car and secured against a rigid spacer; the rigid spacer is then secured in the railway car. Another cylindrical roll is then secured inside the railway car next to the first roll, and another spacer is secured after that roll. This continues for all the rolls in the railway car.
This two-step process has certain drawbacks. It is time consuming and involves excessive work, because the rolls are not loaded in one step. In addition, the spacers used have not typically been successful in preventing compression of the rolls during humping. Finally, because the spacers are rigidly secured, the rolls can suffer damage from contact with the spacers themselves.
Other drawbacks are also present in prior methods of loading railway cars. For instance, some types of spacers crack under the impact of humping. Once cracked, these spacers prove ineffective, requiring replacement or the risk of damage to goods during further transportation.